title: Off-line setup corrections only marginally reduce the number of on-line corrections for prostate radiotherapy using implanted gold markers.
abstract: OBJECTIVE
  To evaluate the efficiency of combining on-line and off-line corrections for the positioning of patients receiving external beam radiotherapy for prostate cancer.
  
  
  METHODS
  Daily portal images were acquired during the treatment of 102 patients to verify and correct the position of the prostatic gland using implanted gold markers. In addition to an existing off-line procedure, on-line corrections were applied in the anterior-posterior (AP) direction only, to limit the increase in daily workload. The possible increase in workload of the combined correction procedure for on-line corrections in either two or three directions was further investigated by simulating the required position corrections for 500 treatments.
  
  
  RESULTS
  The combined correction procedure in AP-direction resulted in a systematic dispersion and random variation of 0.3mm (1 SD) and 1.0mm (1 SD), respectively. Application of off-line corrections during pre-treatment setup reduced the number of required on-line corrections from 22+/-4 (1 SD) to 17+/-4 (1 SD), at the cost of 1.4+/-1.0 (1 SD) off-line corrections. For on-line corrections in two or three directions, application of a combined on-line/off-line procedure did not noticeably reduce the number of setup corrections.
  
  
  CONCLUSIONS
  The on-line procedure is feasible and significantly improves both systematic and random errors to below 1 mm with a limited impact on the workload and treatment time. The application of off-line setup corrections during pre-treatment patient positioning only marginally reduces the number of on-line setup corrections.
authors.affiliation: Radboud University Nijmegen Medical Centre, Department of Radiation Oncology, The Netherlands.
authors.forename: Lisette P
authors.initials: LP
authors.lastname: van der Vight
authors.forename: Emile N J Th
authors.initials: EN
authors.lastname: van Lin
authors.forename: Ilse
authors.initials: I
authors.lastname: Spitters-Post
authors.forename: Andries G
authors.initials: AG
authors.lastname: Visser
authors.forename: Robert J W
authors.initials: RJ
authors.lastname: Louwe
mesh_terms: D000465:Algorithms; D006046:Gold; D006801:Humans; D008297:Male; D009862:Online Systems; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods
chemical_list: D006046:Gold